This invention relates to a method and apparatus for adjusting the quantity of liquid, typically water, deposited on the surfaces of fine granular materials, and a method of preparing mortar or concrete by utilizing the treated granular material.
Fine aggregates comprising river or mountain sand or artificial particles are widely used to prepare cement mortar or lime stone type hydraulic mortar which is used to construct buildings or many other civil structures. When digging or crushing various ores utilized in metallurgy or ceramic industry and coal, fine particles or dust are formed. Further, depending upon the field of use, it is necessary to crush the ores or coal into granules having a predetermined size. When pulverizing or refining these substances or when using them for chemical reactions, fine granules in the form of sludge or the like are often formed. As is well known, these fine granules contain substantial quantity of water adhering to the surface thereof. This is true not only for river or mountain sand but also coal. Especially, in recent years, these substances are dugged by using jet water so that the quantity of the deposited water is considerably large. Even with converter slag which is free from water when it is formed, water is used to collect it. Moreover, as these materials are stored in the outdoor they are wetted by rain, dew or snow. Such wet particles can not be used directly. For example, when sintering or converting these materials to coke, and even when they are directly charged to a furnace, it is necessary to preliminally dry them before actual use. This requires extra heat energy, i.e., fuel. As will be described later in more detail, when a fine aggregate composed of river or mountain sand is used for the preparation of mortar or cement, the quantity of the deposited or surface water is an important factor which influences the quality of the product. Although the composition and particle size of the sand also influences the quality of the product, so long as sand collected from the same source is used it is easy to utilize the sand having the same composition and particle size and it is rare to admix sands from different sources. When the sand contains particles of different size it is easy to classify them into fine, medium and coarse particles with a sieve and a small difference in the particle size does not result in a great difference in the quality of the product. However, the quantity of the surface water varies greatly depending upon the source, the methods of collecting, conveying and storing the sand. Moreover, the specific surface area of the fine particles of sand is large so that the relative quantity of the deposited water is large. Moreover, sand contains water in the interstices of the sand particles which varies from time to time depending upon weather conditions. More particulary, when sand from the same source is piled up on the ground, its water content varies at top and the bottom, and in the morning and at the noon. When preparing cement mortar or concrete by using a fine aggregate, the ratio of water to cement (W/C), the ratios of cement to fine aggregate (C/g) and the ratio of cement or sand to a coarse aggregate (S/G or C/G) have a great influence upon the strength of the resulting product, fluidity, moldability and workability. Thus, when an excessive quantity of water is incorporated, segregation and bleeding are inevitable, thus decreasing the mechanical strength of the product. On the other hand deficient water impairs moldability and pouring property, so that even when vibration or pressure is applied at the time of molding or pouring it is difficult to obtain a dense structure which also decreases the mechanical strength. As above described, notwithstanding the fact that it is essential to select adequate W/C, etc., as the quantity of the deposited water varies greatly and as it is difficult to simply and accurately measure the quantity of the surface water, it is difficult to realize ideal ratios W/C and S/C, etc. Although it has been proposed to completely dry the fine aggregate or to measure the weight thereof in water, such methods are not suitable at the field where a large quantity of sand is used. More particularly, the former method requires a large quantity of heat energy and time and the latter method requires a step of perfectly permeating water into sand to drive off air according to JIS (Japanese Industrial Standard) it is prescribed to immerse the sand in water for 24 hours and a step of draining the water contained in the sand.